Field of the Invention
The present invention generally relates to a refrigerant-transporting hose and particularly to such hoses for use as piping of car coolers, air conditioners and the like which are employed in automotive vehicles.
Discussion of the Prior Art
Referring to FIG. 5, there is shown a conventional hose for transporting or conducting a refrigerant such as flon gas. The hose has a three-laminated or -layered structure consisting of an inner and an outer rubber tube 101, 103 and a reinforcing fiber layer 102 interposed between the inner and outer tubes 101, 103. The inner tube 101 is formed of acrylonitrile-butadiene rubber (NBR), chlorosulfonated polyethylene rubber (CSM) or the like, the reinforcing layer 102 is formed of polyester fiber or the like, and the outer tube 103 is formed of ethylene propylene diene rubber (EPDM), chloroprene rubber (CR) or the like. Reference numerals 115 designate spiking holes formed through the outer rubber tube 103 to communicate the reinforcing fiber layer 102 with outside space. The spiking holes 115 serve to relieve a fraction of the refrigerant which has permeated the inner rubber tube 101, into the outside space, thereby preventing the hose from being swollen due to the refrigerant gas otherwise trapped between the intermediate fiber layer 102 and the inner and/or outer rubber layers 101, 103. Thus, the hose is free from the problem of separation or peeling of each of the three laminates (two tubes and one layer) from the others due to the trapped refrigerant gas.
Since the hose as a whole is formed of rubber materials except for the reinforcing fiber layer 102, the hose has a high flexibility. Accordingly, the hose can be handled with ease, for example in providing a refrigerant-using device with piping. On the other hand, rubber materials have a comparatively high gas permeability, that is, a comparatively low gas impermeability. Thus, the rubber hose suffers from the problem of progressive leakage of the refrigerant gas conveyed therethrough. Therefore, it is necessary to often charge the refrigerant-using device with the refrigerant for compensating for lost fractions to maintain an optimum cooling capacity of the device. It goes without saying that that is very troublesome.
Recently, there is a tendency that refrigerant discharged from the compressor of a cooling system for an automotive engine has raised temperature, which tendency results from raised speed of rotation of the engine. There is also a tendency that ambient air around an engine has increased temperature, which tendency results from small-sized engine room. Thus, it is required that refrigerant-transporting hoses have an excellent heat resistance. However, the above-mentioned conventional rubber hose has the problem that cracks are likely to be produced in the inner rubber tube if the hose is used at raised temperature for a long period of time. That is, the hose does not have a reliable quality. In the case where hoses are formed of a rubber with a high heat resistance, such rubber has an unsatisfactory gas impermeability, resulting in the hoses produced with a low gas impermeability even as compared with the above-mentioned conventional hose.
As is apparent from the foregoing, the conventional hose is satisfactory with regard to flexibility, but unsatisfactory with regard to gas impermeability or heat resistance.
In the background described above, it has been proposed to form the inner tube of a hose of nylon 6, a resin material which is excellent in gas impermeability and heat resistance. However, the material has a high regidity, and when used for producing hoses the material extremely lowers the flexibility of the hoses. Thus, nylon 6 is not suitable for practical use. In the case where a resin with a lower rigidity, such as nylon 6-66 copolymer and nylon 6-12 copolymer, is used to impove the flexibility of hoses, such resins have a melting point considerably lower than nylon 6 and do not satisfy the requirement of sufficient heat resistance.
Thus, there has not been provided a refrigerant-transporting hose which is satisfactory all with regard to gas impermeability, flexibility and heat resistance.